CHAPTER 3 SECTION 3

Gas Behavior

Measuring Gases

Gases can easily contract of expand. Due to this it is helpful to know the volume, temperature, and pressure of a gas.

Since gas particles move and fill the space available, the volume of a gas is the same as the volume of its container.

Temperature is a measure of the average energy of random motion of the particles of a substance. The faster the particles are moving, the greater their energy and the higher the temperature.

Measuring Gases

Gas particles constantly collide with one another and with the walls of their container. As a result, the gas pushes on the walls of the container.

The pressure of the gas is the force of its outward push divided by the area of the walls of the container. Pressure is measured in units of pascals (Pa) or kilopascals (kPa).

Measuring Gases

The firmness of a gas filled object comes from the pressure of the gas. For example, the air inside a fully pumped basketball has a higher pressure than the air outside. This higher pressure is due to a greater concentration of gas particles inside the ball than in the surrounding air.

Concentration is the number of particles in a given unit of volume.

When you see a deflated ball it’s because the pressure inside the basketball drops until it is equal to the pressure outside the ball.

Pressure and Volume

In the 1600s, Robert Boyle measured the volume of gases at different pressures. Boyle found that when the pressure of a gas at constant temperature is increased, the volume of the gas decreases. When the pressure is decreased, the volume increases.

This relationship between the pressure and the volume of a gas is called Boyle’s Law.

Pressure and Volume

Boyle’s law helped researchers using high-altitude balloons. Researchers fill the balloons with only a small fraction of the helium gas that the balloons can hold.

As a balloon rises through the atmosphere, the air pressure around it decreases and the balloon expands. If the balloon was fully filled at takeoff, it would burst before it got very high.

Pressure and Temperature

The faster gas particles move, the more frequently they collide with the walls of their container and the greater the force of collisions.

When the temperature of a gas at constant volume is increased, the pressure of the gas increases. When the temperature is decreased, the pressure of the gas decreases.

Constant volume means that the gas is in a closed, rigid container.

Volume and Temperature

Jacques Charles started a new sport where people would take to the skies in hydrogen balloons.

Charles found that when the temperature of a gas is increased at constant pressure, its volume increases. When the temperature of a gas is decreased at constant pressure, its volume decreases. This principle is called Charles’s Law.